1) Field of the Invention
The present invention relates to an apparatus for measuring a concentration of an optically active substance in an object to be inspected without causing any harm to the object. Particularly, the present invention relates to an apparatus for measuring the glucose concentration in the blood, that is, a blood sugar level.
2) Description of the Related Art
It is indispensable for a serious diabetic to grasp own blood sugar level. This is because of two major reasons. One, at present there is no complete remedial medicine for the diabetes. Second, the diabetic can control his own the blood sugar level only by taking a dose of insulin if there an increase in the blood sugar level, or by intake of glucose if there is a decrease in the blood sugar level.
Most of the methods currently employed for self-measurement of the blood sugar level harm (or attack) the patient, because, in most of these methods the blood is collected from the tip of the finger or arm with a syringe. Once the blood is collected, the blood sugar level is measured based on decomposition of the glucose contained in the blood using a glycolytic enzyme. These methods are quite accurate because the blood sugar level is measured directly from the blood. These methods will be referred to as “attacking methods”.
Some patient may however need to measure blood sugar level a few times per day, for example, after every meal. If the attacking methods puncture the body of the patient, physical pains as well as mental anguish in blood collection may constitute a great burden to the patient. Further, the attacking methods are not suitable monitoring of the blood sugar level continuously. In other words, it is not possible to monitor the blood sugar level when the patient goes to sleep.
There are proposed methods of measuring the blood sugar level without collecting the blood. Since there is no need to collect the blood, these methods do not harm the patient. Some of these methods employ a body fluid such as sweat, and some measure urine sugar. Glucose amount such as in sweat or urine may however be incomplete in correlation with blood sugar level, and the measurement of blood sugar level may be inaccurate. These methods will be referred to as “non-attacking methods”.
Many non-attacking methods proposed principally employ infrared rays of light. Among varieties of methods, some employ a light absorbing characteristic of glucose, and some, a back scattering characteristic of glucose.
A disclosed concentration measuring apparatus employs an optical rotatory tendency of glucose. As glucose has a tendency to optically rotate incident light, the concentration measuring apparatus is adapted to calculate a concentration of glucose by using an equation (1), such that:θ=αCL   (1),where θ is an optical rotation of light incident on glucose, α is an optical rotation coefficient of glucose, C is the concentration of glucose, and L is a length of optical path (see Japanese Patent Application Laid-Open Publication No. 2001-356089).
In reality, however, glucose concentration of blood in physical body is as low as from tens to hundreds mg/dl, in addition to the presence of various absorbing substances, scattering substances, etc. in blood, as well as in skin and other physical tissues. It is therefore very difficult to precisely measure glucose concentration in consideration such as of absorption and scattering of light. The blood sugar level generally indicates glucose concentration of blood, and even in the case using the optical rotation tendency, it is difficult to actually determine the length L of optical path across blood regions.